1. Field of the Invention
The present invention relates to a display unit of an input integral type for a handwriting input used in an office automation (OA) equipment and an audio visual device.
2. Description of the Related Art
Recently, requirements for a display unit having a large size and a large display capacity have been increased as an information-oriented society is advanced. A cathode ray tube (CRT) called the present king of a display is developed to satisfy these requirements. The CRT is more precisely constructed and is large-sized in development. For example, the CRT approximately has a size of 40 inches at its maximum in the case of a direct viewing type and has a size of 200 inches at its maximum in the case of a projecting type.
However, the problems of a weight and a depth of the CRT are more serious in realization of the display unit having a large-sized structure and a large capacity. According, it is very desirable to provide a method for basically solving these problems.
A plane type display unit performs a displaying operation using a displaying principle different from that of the general CRT. The plane type display unit is steadily researched to provide a high display quality required for a high vision and a display for a high performance engineering work station (EWS) although the plane type display unit at the present time is widely used for a word processor, a personal computer, etc.
For example, the plane type display unit is constructed by an electroluminescent panel (ELP), a plasma display panel (PDP), a fluorescent display tube (VFD), an electronic display unit (ECD), a liquid crystal display unit (LCD), etc. In these display units, etc., the liquid crystal display unit (LCD) is most promising in consideration of easiness of realization of a full color and matching with a large scale integrated circuit (LSI). Accordingly, a technique of the LCD is most greatly advanced.
The LCD is generally divided into an LCD of a simple matrix driving type and an LCD of an active matrix driving type. The LCD of a simple matrix driving type has a structure for sealing a liquid crystal into an XY matrix type panel in which a pair of glass substrates are opposed to each other such that electrodes each formed in the shape of a stripe are perpendicular to each other. The LCD of a simple matrix driving type performs a displaying operation by using rapid responsive display characteristics of a liquid crystal.
In contrast to this, the LCD of an active matrix driving type has a structure for directly adding a nonlinear element to a picture element. The LCD of an active matrix driving type performs a displaying operation by positively using nonlinear characteristics such as switching characteristics of each of elements. Accordingly, no LCD of an active matrix driving type greatly depends on the display characteristics of a liquid crystal in comparison with the LCD of a simple matrix driving type. Accordingly, it is possible to realize a display unit providing a high contrast and a high speed response.
The above nonlinear element is divided into nonlinear elements of two and three terminal types. The nonlinear element of a two-terminal type has a structure of metal-insulator-metal (MIM), a diode, etc. In contrast to this, the nonlinear element of a three-terminal type has a thin film transistor (TFT), a silicon metal oxide semiconductor (Si-MOS), silicon-on-sapphire (SOS), etc.
In view of uses of the LCD in their markets, a lap top personal computer and a palm top personal computer having the LCD of a simple matrix driving type and the LCD of an active matrix driving type are promising as goods for extending the markets.
In particular, an input device of information in important in a portable information remote terminal such as the palm top personal computer. In this input device of information, a handwriting input function is strongly required to omit a space for a keyboard.
In the general display unit, a tablet digitizer is mainly arranged outside a liquid crystal panel to fulfill this handwriting input function so that the inputting position of a pen is detected by a tablet. This tablet is constructed by an electromagnetic induction system, an electromagnetic giving-receiving system, a resistance pressure sensitive system, an electrostatic coupling system, an acoustic system, an optical system, etc.
FIG. 1 shows one example of a tablet of an electromagnetic induction system.
As shown in FIG. 1, the tablet is constructed by a conductive pattern 1 and an exciting or cursor coil 2.
When diodes 5 are sequentially turned on by an X-axis ring counter 3 and a Y-axis ring counter 4, a voltage corresponding to each of these diodes is outputted from a common terminal M. When an alternating current signal is simultaneously applied to the cursor coil 2, an induced electromotive force is generated on a scanning line.
As a result, a composite wave provided by combining the turning-on voltage with the induced electromotive force is generated from the common terminal M. The composite wave is A/D-converted and is additionally inputted to a maximum value detecting circuit. This maximum value detecting circuit has a function for detecting a maximum amplitude value of the composite wave. The maximum value detecting circuit also has a function for selecting a larger one of electromotive forces on right-hand and left-hand scanning lines adjacent to a scanning line corresponding to the maximum amplitude value. Thus, it is possible to detect a cursor position by these functions.
FIG. 2 shows one example of a tablet of an electromagnetic giving-receiving system.
This electromagnetic giving-receiving system includes a tablet 6, an address portion 9 connected to the tablet 6, a giving-receiving selector 10, a sensor 11 and a driver 12. The sensor 11 and the driver 12 are connected to a controller 13 and are selectively connected by the selector 10 to the address portion 9.
An alternating current is applied onto a matrix line on the tablet 6 so that electromotive force is absorbed into a resonance circuit or coil 8 arranged within an indicator 7. At the next moment, the matrix line of the tablet 6 functions as a sensor and detects an electromagnetic wave generated by the resonance circuit or coil 8 within the indicator 7.
FIG. 3 shows one example of a tablet of a resistance pressure sensitive system.
This resistance pressure sensitive system has an interlocking switch 19. Two resistor sheets 14 and 15 respectively have electrodes 17 and 18 and are stuck to each other with a clearance. The sheets 14 and 15 come into contact with each other by applying pressure onto these sheets so as to generate an electric potential. X and Y coordinates of this pressure are detected by the generated potential. Namely, a direct current voltage is applied to the resistor sheet 15 for an X-axis and a voltage generated by pressure in the resistor sheet 14 for a Y-axis is taken out so that an X-coordinate of this pressure is detected. The X and Y coordinates of pressure are alternately detected by applying voltages to the sheets on the X and Y axes by time division.
FIG 4 shows one example of a tablet of an electrostatic coupling system.
In this electrostatic coupling system, rectangular waves having different phases are applied to both ends of electrodes 21 and 22. Positions of an optical pen 24 on X and Y axes are alternately detected by a switch 23. The pen 24 is electrically connected to a phase detecting circuit 27 through an amplifier 25 and a filter 26. X and Y coordinates of the pen 24 are provided by detecting a signal phase determined by the position of an ITO film 28 through the pen 24.
In a tablet of an acoustic system, the position of an optical pen is provided by detecting a propagation time of a sound wave transmitted in the air or a surface wave propagated on a tablet surface, and an arrival time of a reflected wave.
In a tablet of an optical system, a light emitting element is arranged on one of X and Y axes and a light receiving element is arranged on the other so as to detect a light interrupting position.
The above-mentioned tablet detecting systems have the following disadvantages.
(1) In the electromagnetic induction system, relatively high resolution can be obtained, but power consumption is large and the weight of a display unit is heavy and the display unit tends to be influenced by a magnetic field.
(2) In the electromagnetic giving-receiving system relatively high resolution can be obtained, but power consumption is large as a demerit.
(3) In the resistance pressure sensitive system, cost of the display unit is reduced in comparison with the other tablet detecting systems, but there is a problem about the uniformity of a resistance value and resolution is bad and the sheets tend to be damaged so that durability of the display unit is bad.
(4) In the electrostatic coupling system, relatively high resolution can be obtained, but it is difficult to set the pen 24 to be wireless and power consumption is relatively large. Further, the display unit tends to be influenced by static electricity.
(5) In the acoustic system, the structure of a detecting circuit is complicated and the display unit tends to be influenced by a circumferential environment.
(6) In the optical system, resolution of the display unit is bad.
As mentioned above, it is impossible to sufficiently provide a satisfactory display unit in each of the above-mentioned tablet detecting systems. Further, each of these tablet detecting systems is arranged in an upper or lower portion of a liquid crystal panel so that inputting and displaying positions of characters, etc. are shifted from each other in accordance with a parallax.